Concussions occur as a result of imparted linear and rotational accelerations to the brain.

Because of modifying factors (e.g., concussion history, neck strength, anticipatory reaction and varying magnitudes, frequency, and locations of impact), there is currently no known threshold for concussive injury.

Metabolic changes that occur in the animal model and thought to occur in humans include the following:

A relative decrease in cerebral blood flow in the setting of an increased requirement for glucose (i.e., increased glycolysis). This mismatch in the metabolic supply and demand may potentially result in cell dysfunction and increase the vulnerability of the cell to a second insult.

Complications of Concussion

Concussion may cause a wide range of short- or long-term complications, affecting thinking, sensation, language, or emotions. These changes may lead to problems with memory, communication, personality changes, as well as depression and the early onset of dementia. Other complications of concussion are also addressed in this section.

Prior concussions may increase risk for subsequent concussions.

Postconcussion syndrome

Persistent postconcussion symptoms lasting 3 months or longer

Indicator of concussion severity

Precludes RTP while present

Increased risk of depression

Convulsive motor phenomena

Tonic posturing or convulsive movements within seconds of the concussion

Dramatic, but usually benign

Require no management beyond on-field ABCs

No anticonvulsant therapy required

Posttraumatic seizures

Seizures occur days to months after concussion

Does require seizure management and precautions

Usually requires anticonvulsant therapy

Second-impact syndrome

Occurs within minutes of concussion in athlete still symptomatic from prior brain injury, which can be earlier in same event.

Initial signs and symptoms do not typically manifest until decades after trauma received (ages 40–50 yr).

A small subset of individuals with chronic traumatic encephalopathy have developed chronic traumatic encephalomyopathy, a progressive motor neuron disease characterized by profound weakness, atrophy, spasticity, and fasciculation similar to amyotrophic lateral sclerosis.

Depression

Increased risk after a history of multiple concussions

May predate concussion and/or occur independent of concussion.

Athletes with depression who later sustain concussion may experience worsening symptoms.

Mild cognitive impairment

Increased risk later in life after a history of multiple concussions.

May predate concussion and/or occur independent of concussion.

Multiple concussions have been associated with an earlier onset of mild cognitive impairment.